1. Field of the Invention
The present invention relates to an automatic door system, and more particularly to an apparatus for controlling such a system.
2. Description of the Prior Art
A typical automatic door system has a door coupled with and driven by a belt extending from a drive pulley to its driven pulley. The drive pulley is driven by a reversible motor. Controlled rotation of the reversible motor provides automatic opening and closing of the door. In the Japanese Patent Public Disclosures 19366/80 and 28982/81, there is disclosed a prior art apparatus for controlling such a door system which employs, as means for tracking the movement of a door, a revolution sensor mounted on the shaft of the door drive motor for generating signals indicating the number of revolutions of the motor.
However, the above sensing of the door movement is an indirect one, and ignores the error in the transmission mechanism from the motor to the door to be driven. For example, a slip sometimes occurs between the shaft of the motor and a transmission mechanism in the form of, for example, a belt which extends to a drive pulley and/or between the drive pulley and a belt extending from the drive pulley and its driven pulley. Such slips introduce an error between the sensed door position and the actual door position. This might result in collisions of the door against its counterpart or a wall, or stopping of the door before it reaches its stroke end.
Further, continued running of the motor occurs when the transmission mechanism such as a belt is cut. This will burn the motor coils since the motor for driving a door is designed to be short-time rated.